Singularity
by brainmush
Summary: Who would have thought that jumping off a building would become so complicated? A jolly good yarn spanning the whole of time... and a small portion of London. Contains some spoilers for "The Reichenbach Fall" and "The Empty Hearse".
1. Chapter 1: Quantum Leap

"No, no..."

John's voice buzzed in his ear.

He looked down at the street below him.

Of course, he had prepared for just such a situation. Each of the thirteen possible outcomes of his meeting with Moriarty had been accounted for, and planned down to the last detail. There was no way that he could lose.

The crash mat had been fully inflated. One of his assistants on the ground had given the signal that it was okay to drop. John was in the perfect position. All Sherlock needed to do was let go.

The phone skittered along the roof behind him.

Everything had been said. Nothing more needed to be done.

He slipped silently from the rooftop and into nothingness.

It was all a little disappointing, Sherlock thought. Everything had slotted into place much too easily. In the end, Moriarty had provided him with quite an underwhelming conclusion to what he had hoped to be an entertaining game.

The great Sherlock Holmes, cheating death with a well-placed building and a bag of air.

_How boring_, he thought.

He braced himself for impact, and his world was swallowed up by blue darkness as the curtain was drawn on his "final" case.

However, as he sank into the shadows, he couldn't help but feel that something was amiss. It was none of his doing, of course - his plans, as ever, were faultless.

But he had expected the feeling of falling to have stopped by this point. He had yet to reach any form of physical resistance, disregarding the air rushing past him as he plummeted downwards.

In addition, there were... noises. Mechanical noises buried not so deep within the blackness that surrounded him; noises which were not muffled by any means. And smells - the smell of sulphur, electrical fires...

As moments flickered past, Sherlock's mind wrestled with the information his senses were providing him.

No sensation of landing. The combined sounds and smells were those one would expect to find... where? A poorly maintained factory? A laboratory of some kind?

No. Sherlock shook those thoughts from his mind. He had fallen - was still falling - from the roof of St. Bart's. Whatever he was falling into hadn't been there before he had gone up there to meet with Moriarty, so clearly it needed to be mobile.

A laboratory on wheels? That was stupid. A military craft, then? There was no vehicle he had ever encountered that would satisfy all of the criteria. In this situation, he had no option left but to deduce that it was, in fact, a vehicle he was unfamiliar with.

It was a bitter deduction for him to swallow.

Regardless, it would have to be a very large vehicle, and - judging by the smells - one in some considerable degree of distress.

So, to recap, instead of falling into a soft, safe inflatable bag, Sherlock was instead hurtling into a massive, unidentified, and potentially dangerous moving machine.

"That's just wonderful," he muttered to himself.

"Ahaha!"

To Sherlock's surprise (another painful revelation - how tedious this day was becoming), a man's voice broke through the gloom.

"A visitor! An unexpected one at that. And I thought I locked that door too," said the voice. From some distance away - Sherlock guessed at between ten and twenty feet from him, a ridiculous measurement which confounded him to no end - there was a flash of sparks from some minor electrical explosion. Sherlock's mind was racing even faster than usual.

Suddenly, a grating, groaning sound swelled up and out from unplaceable spot in the dark. There was another display of sparks, a snapshot of a cavernous, impossible room as it lit up for a fraction of a second, and then the world around Sherlock lurched.

A huge flat wall grazed past him, and seemed to curve up around him as he continued to fall, swooping up and beneath his body. The side of his calf kissed the hard surface first, sending him tumbling down and along the wall as it quickly became a floor. He barreled a few feet further before colliding with a set of railings and, finally, coming to a halt.

A final spray of light exploded in the distance before the chamber around him became fully illuminated. Sherlock's vision blurred as he struggled to acclimatize to his surroundings.

A huge moving pillar dominated the centre of the room (Room? Sherlock frowned). It was surrounded by a mess of screens and switches that tangled together in a manner that defied all common sense. It was clear to see that this was a control room of some sort, though for what vehicle, Sherlock still couldn't say.

He pouted and tried to focus.

A frustrating distraction emerged in the form of a young-looking man in a tweed jacket. The tweed man teetered out from behind the pillar and fiddled about with some of the wires dangling from one of the control panels.

"Sorry about that," said the man. He straightened his bow tie as he continued to rummage around in the wires. His expression lit up in a split second, as he drew a slim instrument from between the cables and gave it a preparatory swish. It made a pleasant whirring sound, but that still didn't make Sherlock feel any happier about the situation. The man in tweed continued.

"The old girl's a bit temperamental when it comes to phasing through interdimensional subspace rifts at the moment. Takes a while to get her back in full working order," he said, heartily slapping a one of the control units around the pillar. There was yet another shower of sparks, though this time it was, at least, reassuringly smaller than the last. "Mind you, I don't suppose there are many people that'd be all too happy about having all their atoms scattered across the whole of time and space and then snapped back together. Never mind, we're all in one piece." He paused, and squinted at a flickering monitor that hung limply from a single cable. "Well, mostly in one piece. I think. Anyway, I'm alive, the TARDIS is still here, and - " he beamed over at Sherlock, " - and we have a guest. And _you're _alive too. Brilliant! Day keeps getting better all the time!"

Shakily, Sherlock got to his feet. He brushed his hair from his face and donned a sour expression.

"A time machine," he spat. "I fell into a... a time machine?"

"A hello would have been nice," said the man. He strolled forwards and stretched out his hand for Sherlock to shake. "I'm the Doctor."


	2. Chapter 2: Bite

The Doctor made a final scan of the auxiliary quantum capacitor module with a swipe of his sonic screwdriver. It made a pleasing whirring noise.

"Well," he chirped. "Everything seems to be in working order. But I guess that's pretty obvious, really. If it wasn't, we probably would have asphyxiated by now. Or something like that."

He paused, and waved his hand a fraction in the direction of the brooding man nestled in the corner. There was no reaction.

"Or we might have exploded. The TARDIS explodes a lot more frequently than people might think. And explosions aren't any fun at all. Well, not when you're in the middle of them," said the Doctor. "That happens quite a lot too. Would you like a cup of tea? I've got a brew on. And biscuits. Might be a bit chewy though. Picked them up back in the 1950s. Helped a charming young lady deal with a nasty Cyberman problem, and I got cookies. Pretty good deal, I'd say."

"I am _thinking_," the brooding man glared into middle distance. "Shut up."

"So I noticed," the Doctor smiled. "You're quite the thinker. Lots of stuff up there," he said, tapping his temple. "You guessed the TARDIS was, as you put it, a 'time machine'. In a single glance! Most people are still trying to work out what that means even after I've explained it. That's pretty impressive stuff. Unless we've met before, that is. Have we met before?"

"No, we haven't," the man snapped. "And for your information, I am not 'most people'. Now shut up."

The Doctor chuckled and produced a cookie from his jacket pocket. He tossed it in his mouth, still grinning to himself. "Any more outbursts like that and we might not have enough room in here for both our egos." He produced another cookie and trotted over to the man in the coat. He tapped him on the shoulder with the biscuit. "And by the way - what's wrong with being 'most people', eh? They're fascinating things. Quite remarkable in little ways. Very... persistent."

The broody man turned and glowered at him. "Do you _ever _shut up?"

"Not really, no," the Doctor said. He brandished the cookie at his guest. "Hungry?"

"Shut up." The cookie was swatted from his hand and danced across the floor. "_Shut up_."

"Moody." The Doctor's eyes lit up. "But I guess this is all a bit much for you. You're a clever man - anyone can tell that - but you're not very elastic when it comes to thinking outside your little box. You're from... what, twentieth, twenty-first century Earth? Years and years before you guys discover time travel."

The man in the coat looked furious.

"But you're not going to let a little thing like impossible science stop you, are you? See, I knew I liked you when you came in! Oh, I like this. You're fantastic, you are. Brilliant!" The Doctor clapped and rubbed his hands together, twirling away on his heels. "You're working it all out. Just because you've never encountered time travel doesn't mean you're going to let it beat you. You're going to unravel this even if it kills you. You're like me! Only not quite as handsome."

More glaring. The man in the coat was very good at glaring.

"Sorry about that," he said. "But it's fascinating, really. Even though all this," he spread out his arms at the whirring, beautiful mess that was the TARDIS, "is completely beyond your comfort zone, you're working it all out. You don't need to ask questions because you're finding all the answers in your head! So... so go on then. What have you got so far? Ooh, this feels kind of like a test. I feel like a teacher. Haven't done that in a while - "

The man's fist connected with his jaw, sending him sprawling across the floor.

"Ow. That hurt."

The man in the coat stepped up to him and loomed overhead.

"This is a time machine," he growled. "A vehicle that's larger on the inside than it outwardly appears, and can be rendered invisible."

"Good, good. How'd you work that out?"

The man sneered. "The dimensions of this room alone is too large to fit in the approximate space that I had left to fall. Also, as I descended, I couldn't see the craft until I was inside it."

The Doctor nodded. "What about the time machine part?"

The man in the coat seemed to ignore him, and continued. "You're a renegade alien who commandeered the time machine illegally." As the Doctor opened his mouth to speak, he hurriedly explained. "Though you look and superficially act like a human, your reactions, mannerisms and... choice of clothes imply a very different cultural experience to anything Earth has to offer. You're practically a walking cartoon character.

"The craft has clearly been shoddily repaired multiple times, in a way that the original designers didn't intend - obviously it hasn't been touched by an actual professional with certified experience in maintaining it for a very long time. Any normal person who had damaged such a valuable form of transport wouldn't risk trying to repair it by themselves, or leave it in the hands of the inexperienced. You clearly don't want to contact any officials with more knowledge in that field for some reason. A criminal doesn't want to return the things they've stolen."

"Impressive. Good reasoning," said the Doctor. "But the TARDIS is borrowed. Not stolen. There's a very distinct difference."

The man in the coat seemed amused at that. There was something in his expression, something in that demeanour and that curious way he seemed to work everything out so seamlessly that was oddly familiar to the Doctor, but he was struggling to remember who the man reminded him of. Himself excluded, of course.

"As for my presence here," the familiar man continued with a tone that dripped with sarcasm, "let me guess - you've lost your pet Martian, or the moon's disappeared and you need my help to find it again."

The Doctor wrinkled his nose. "Which moon?"

There were no words uttered for several long seconds. "THE moon," The man spluttered, as though this explained anything. Spying the incredulous expression spreading across his host's face, however, the man's cheeks flushed a slight shade of pink. "Shut up."

"Anyway," the Doctor smiled genially and dipped his hand back into his pocket, slightly disappointed to discover that nothing but the crumbs of cookies long since gone remained. "You did very well. B plus, have a gold star or something. You got every point absolutely one hundred percent correct. Except for the whole 'needing your help to find the moon' thing. Actually, the whole moon situation was a bit wrong, but I'll let you off, because I'm nice."

The man sighed. "I didn't _actually _mean you wanted me to help you find the moon," he said. "How do I put it in a way you could understand? You want me to help you solve a problem. That's why you brought me here."

"Only I didn't. It was an accident. Pure coincidence," the Doctor said. He took his sonic screwdriver firmly in hand and twirled around in his fingers. He pressed it, and it made the little whirring noise again.

"I don't believe in coincidence," the man grumbled.

"Nor do I," the Doctor chuckled, gazing at the little green light emanating from his screwdriver. "On a completely unrelated and terribly unimportant note, I never did catch your name."

Clearly unimpressed at the sudden drop in intelligent conversation, the man rolled his eyes. "Sherlock Holmes. Consulting detective."

"That's it!" The Doctor hopped into the air and scuttled away to the TARDIS control panel. He pulled a few levers, flipped a dozen or so switches and watched as his wonderful blue box roared and shuddered to life. "I knew it!"

"Knew what? What on earth are you talking about?" Sherlock Holmes was nearly knocked off his feet as the TARDIS rumbled all around them.

"You! I thought I knew you. There was something about you I was sure I knew, and I didn't know what, but then I scanned your bio-readings and it came up with a match. A match! You share a key genetic strand with someone I've met before. But you don't just share it. Oh no, it's identical. It's exactly, exactly the same. Oh, it's uncanny," the Doctor giggled, flipping yet more switches, turning cranks, pressing buttons. "It's practically impossible."

Sherlock's eyebrows raised. "You mean to say there's another Sherlock Holmes out there?"

"Quite the coincidence, wouldn't you say?"

Both Sherlock and the Doctor grinned.


	3. Chapter 3: Holmes Sweet Holmes

Time travel was theoretically impossible. Time travelling in a spatially questionable, invisible box captained by a madman with a bow tie was verging on the ridiculous.

Sherlock tapped one of the monitors protruding from the central pillar of the TARDIS. The whole machine seemed to warble in response around him.

It was clear to him that this was no figment of his imagination. Though he knew of many chemicals that were able to replicate more than simple visions - substances that could trick the consumer to believing that they had felt textures, smelled scents or tasted fabricated flavours - he had studied each of these concoctions enough to be able to tell the difference between their effects, and the experiences of reality.

Unfortunately, this gave him very little option but to accept everything happening around him to be true: from the stupid machine to the stupid man operating it, and the stupid method of his own stupid arrival - everything.

This did not sit right with him at all.

The Doctor had left him alone in the main control room. This was quite a stupid act of faith on the Doctor's part, though Sherlock supposed there would be little to gain from sabotaging the man's ship while he was gone. Apparently, he needed to "get things ready" before they left, though exactly what he had to prepare, Sherlock could only speculate.

The fool was still clinging onto the preposterous notion that there were multiple Sherlock Holmeses wandering around.

"Holmeses," he muttered. "Holmesii? Holmesae?"

Another impossibility. Sherlock was even less inclined to accept this particular claim. More than one Sherlock Holmes was quite a lot more than the universe needed. Many people would argue that just the one Sherlock was more than the universe needed.

He made another lazy circuit of the control room.

Being completely impossible and all, time travel had never been at the top of Sherlock's list of interests. However, the past few minutes in the TARDIS had been an ample enough period of time for him to get a grasp of the basics.

Basically, the TARDIS seemed capable of travelling across both time and space, and only variants of those two dimensions of existence. Admittedly, those two planes were quite expansive, but unless Sherlock's understanding of them were incorrect (and obviously they were not) this still meant that the approximate probability of finding a person bearing the same name and the exact biological structure as himself was somewhere around zero percent.

And yet, as absurd as the Doctor's claim was, and as many basic laws of physics it demolished, there was no reason he could find to suggest that the Doctor himself didn't believe it to be true.

As if on cue, the embarrassingly cheerful time traveller reappeared from a side door, donned in an alarming amount of tweed - moreso even than before, though Sherlock found such a notion hard to swallow - and sporting a deerstalker hat.

"How do I look?" The Doctor grinned and flapped the little tweed cape he had wrapped around his shoulders. "Thought I'd try to dress the part. You know, muscle in on the whole Sherlock Holmes look."

"How is that anything like what I wear?"

The Doctor squinted at Sherlock before looking back down at his own costume. "It doesn't," he said, finally. "Not a bit. Anyway, are we going to hang around here all day talking about your bad fashion sense, or are we going to go out and find impossible things? Come on now, don't be dull."

Sherlock watched as the Doctor headed to the TARDIS's main entrance and opened the door up onto a dark place, heavy with fog. As the new world beyond the door was revealed to him, Sherlock's lips stretched out into a long, unimpressed line.

"Of all the places in all of time and space," said Sherlock, "you bring me back to London."

"Yes. Exactly. London, England, Planet Earth," the Doctor said. "No better place to start the hunt for a consulting detective."

* * *

The hush of night seeped through the cobbled streets of London, stretching shadows out to infinite lengths beneath a blackened sky. This was not an hour for gentle folk; the streets now played host to a far more sinister breed: shady men with glinting knives, huddled away in unseen places, scrambling through the urban wilderness away from the prying eyes of day.

Beneath the gas street lamps, policemen too were patrolling, ever vigilant against the unfriendly forces that shared the midnight hours with them.

A young officer stood at a street corner, shivering to himself and struggling with his matches. His pipe trembled between his lips - a keepsake from his late father, and a reminder of the respectable name he strived to live up to on this, his first night patrol.

His nerves were eating at him. He hurriedly lit the pipe and inhaled sharply, making little puffs of smoke in nervous desperation as he attempted to calm himself down. The tobacco seemed to be doing its job capably, but slowly.

"No reason to panic, Wilbur," he told himself. "You know these streets of old. No surprises lie in store for you this night. Nor any other night," he added quickly.

He continued on his route, pouring his attentions into achieving a steady rhythm of smoke rings with his pipe. Soon enough, he had managed to calm himself down enough to take a more pleasant and relaxed pace. The beginnings of a cheerful expression crossed his face.

Officer Wilbur's feet carried him along the first circuit of his patrol, and a few streets more before he stopped to rest his legs a little.

"Perhaps this isn't so bad," he sighed to himself, slowing to a crawl at a crossroads. He removed the pipe from his lips, feeling a little more confident now. Maybe he could live up to his father's stellar reputation in Scotland Yard after all...

The confidence waned a fraction as a hand tapped him on the shoulder. Officer Wilbur swivelled around to see who was trying to attract his attention.

He was greeted by nothing but a dark and empty stretch of road.

He felt a small chill scamper down his back, and turned back around to seek comfort from his old friend tobacco.

He found his hands empty. His pockets too.

A flash of light caught his eye from down a long, shadowy alleyway. His teeth gritted as the tiny green pinprick of light danced and blinked in the distance.

Gripped by a sudden sense of dread, Wilbur turned and fled.

* * *

Sherlock smirked as he walked back up the alleyway. He took a long drag from a fancy-looking tobacco pipe and exhaled the smoke through his nostrils.

"Where did you get that?" The Doctor cocked his head, clearly disapproving of Sherlock's unhealthy little habit. Having finished scanning the area, he clicked his sonic screwdriver, blinking out the little green from its tip.

Sherlock sighed and took another long inhalation. He coughed in satisfaction. "A gift," he smiled. "It seems the police are just as quick-witted in this London as they are in my own."

"Strictly speaking, this is your London," said the Doctor. "It's just a little younger than you might remember it. Though, if we're talking in a general sense, it really is your London anyway. Just not directly. It's the other you's yours, on account of the whole 'more than one Sherlock Holmes' thing."

"Mm, yes," said Sherlock. "You did mention that numerous times, before escorting me 'helpfully' to whenever this may be."

"Late nineteenth century. I thought you liked working things out by yourself?"

Sherlock chose to ignore this remark. "I presume we're here to find another Sherlock Holmes, then. I've noticed you're taking us in the direction of Baker Street."

The Doctor shrugged. "I don't remember the names," he said. "Wait, is that where you live?" His eyes brightened at the thought of this. "Do you reckon you live on the same road as Sherlock Holmes?"

"I would find it very difficult not to," Sherlock grumbled.

"Brilliant," the Doctor said, beaming. He hopped backwards and tottered a few more steps down the alley. "Absolutely wonderful. I mean, don't you just love how impossible this all is? The whole of time and space should be coming to bits around us because of how little sense it all makes. But it isn't! Hurry up - I want to see your faces when you meet."

With that, the curious man with the bow tie trotted away into the blackness of another side-street.

Sherlock knocked some the excess ash from his pipe and raised it once again to his lips.

They walked together into the unknown.

* * *

"No, no..."

John Watson shook his head emphatically. This was all wrong. He had seen his friend in many dire situations, but this...

His moustache bristled at the sight.

"Holmes," he muttered. "I fear my warnings may be falling on deaf ears - we have been over this same subject so many times, and yet it has all come to naught - but I must implore you to stop."

Sherlock Holmes, the genius detective and Watson's dear friend for many, many years looked up hazily. A syringe dangled from his fingertips, half-spent and dripping its foul concoction onto the floor. "I daresay you have come to a reasonable conclusion, Watson. Your perceptions are improving by an impressive margin," he smiled. "Your advice does indeed fall upon deaf ears."

As rational and logical a man Holmes usually was, Watson knew there was little point in perpetuating the argument. The man possessed a brilliant mind, but he was as petulant and defiant as a child when he chose to be. The conversation would most likely not move forward if it was not heading in a direction that Holmes wished it to.

"In that case, dare I ask why you summoned me to Baker Street at so late an hour," he sighed.

At that moment, Mrs Hudson emerged into the room carrying an assortment of biscuits and a pot of tea, complete with teacups. Holmes snapped to his feet. "Enough dallying for the night. You see, Watson, I was simply whiling away the time before our guests arrive. By my approximations, they should be here in little more than a few minutes," he explained. Mrs Hudson wordlessly set the tray down as if working by clockwork. "Now," Holmes nodded to the housemaid, "go and wait by the door and let them in when they arrive.

"Watson - do sit down." Holmes pottered to a case he kept on the mantelpiece and replaced his syringe into it. "And please," he added, settling back down into an armchair, "I implore you, try not to be alarmed."

Watson was dumbfounded. "Alarmed?"

"At our guests, yes."

Sinking into his own seat, Watson attempted to fathom exactly what manner of guest Holmes was expecting, to have given such a warning before their arrival.

It did not take long before Watson heard a knock at the door, just as Holmes has predicted. "There they are," the detective said. "Do take a biscuit or a cup of tea, old boy. Make yourself at home. We may be here for some time. I trust this may be quite the singular case."

The curious guests seems to take part in a considerable discussion with Mrs Hudson before she escorted them up the stairs, though Watson was quite unable to tell what was being said. Soon enough, they were greeted by the housemaid once more, who was joined by two gentlemen of a most curious appearance - the first, a tall, severe man in a long coat, and the second, cheerful, and clad in an alarming amount of tweed. Mrs Hudson looked quite unhappy.

"I apologise, Mr. Holmes," she said, shooting daggers at the guests, "but these two men are quite disagreeable in giving their names. They seem quite insistent on acting the fool."

"No worries," Sherlock smiled a most peculiar smile, his fingers steepled. "These gentlemen should be more than capable of introducing themselves."

The man in tweed stepped forward. "Mr. Holmes, a pleasure to see you again. I'm the Doctor, you remember? I'd like you to meet my new friend," he said. "Sherlock Holmes, meet Sherlock Holmes."


	4. Chapter 4: The Game is Afoot

The sonic screwdriver blinked and whirred in the Doctor's hands.

It was fascinating. Absolutely fascinating.

There was absolutely nothing he could find wrong - aside from the rather obvious fact that he was sitting in front of two people who couldn't exist in the same reality. There was no spatial rupturing, no traces of any kind of time displacement - nothing.

Either his screwdriver was in serious need of a tune-up, or he really had stumbled into a mystery.

He nudged Doctor Watson in the arm and winked. "This is a bit of a head-scratcher, isn't it?" he said. "Good job we've got a couple of detectives on the case, eh?"

The good doctor - _the other one_, The Doctor smirked - looked more than a little bewildered at the scene. "I say," he muttered. "I have seen Holmes tackle his fair share of difficult cases in the time I have known him, but... Are you quite sure that this gentleman here...?"

"It's Sherlock Holmes, all right," the Doctor nodded. "To be perfectly honest, I'm not sure I get it either. But it's him. They're the same man - only different."

Watson seemed to be following. It was astounding to see how receptive to new information the man was. From experience, he knew that the best of companions possessed this kind of mental elasticity - not necessarily an advanced intellect, but a willingness to accept the impossible things going on around them. No wonder the detective liked keeping Watson around.

Presently, the detective himself was in a heated, yet largely silent discussion with his impossible counterpart. They studied each other intensely, and spoke with only the bare minimum of verbal communication.

Several minutes of quiet surveillance ticked by before the Victorian incarnation decided to break the silence. "I must say," Holmes smiled softly, lifting a cup of tea to his lips, "I am most fond of your choice of pipe, old boy. New, is it?"

Sherlock's lip twitched. He pressed his hands together and leaned forwards. A few long seconds crawled by. "You prepared tea," he growled.

"I was expecting guests."

With that unremarkable declaration, the pair once again descended into intense wordlessness.

"It's a bit like watching a game of chess," the Doctor mused out loud. "Only without the board and the chess pieces. And it's a lot more boring." He nodded over at Watson. "Are they always like this?"

"I cannot speak for your friend, but... yes, I am afraid so." Beneath his breath, Watson muttered, "Though from this encounter, I daresay every Holmes I have met possesses this selfsame intellectual stubbornness."

"Every Holmes? Wait, are you just talking about these two, or have you met more of them?" The Doctor's eyes lit up.

Watson nodded gravely. "I have only met a handful, but... that may be quite enough Holmeses to be getting along with."

"Holmesii," Sherlock grumbled.

"Holmesae," Holmes deduced.

Choosing to ignore the Holmeses, Watson continued. "I have been introduced to Holmes' brother Mycroft, for one," he said. "That was an... education."

Upon mention of Mycroft, an identical muscle tightened in the cheek of both Sherlocks. "Mycroft," they spoke in unison, with a similarly unimpressed tone.

"Oh," said the Doctor. He did not attempt to hide his disappointment. "So no more Sherlock anomalies wandering around London, then."

"On the contrary," Holmes butted in. "One cannot rule out any possibility without consideration of all the facts. Dr. Watson here may be many things, but seldom is he a source of conclusive evidence."

"Or intelligent conversation," Sherlock sneered.

Watson's moustache flared. The two Sherlocks chuckled to one another.

"Glad to see we're all finally getting on." The Doctor smiled and put a hand on Watson's shoulder. "Now that we've found some common ground, how about we get down to the business at hand? Namely... this." He spread his hands out at the two detectives.

Sharing the briefest of glances with Sherlock, Holmes took to his feet. "In that case, I believe we shall need your TARDIS, Doctor. And the use of your sonic screwdriver, if you would be so kind to assist us." As he spoke, Sherlock too rose from his chair, gathered his coat around himself, and began to walk slowly around the perimeter of the room. "Of course, I am unable to vouch for the other Sherlock Holmes, but if he is as brilliant as I believe myself to be, we may have a plan."

The Doctor was thrilled to see the united enthusiasm. Watson, slightly less so. "TARDIS?" His eyebrows knitted together, moustache rustling as he mouthed the word to himself over and over. "I am finding myself increasingly lost in this muddle of an affair, Holmes."

"It's quite simple. The TARDIS is a time machine, my dear Watson. The Doctor is a man from another world, and this gentleman here is an anomalous incarnation of myself, presumably from about a century or so in the future, though I am merely speculating at present; I come to this conclusion from the unfamiliar, synthetic structure of his coat and shoe soles alone, which is hardly the most accurate method of deduction," Holmes explained. "At any rate - I am proposing, with the Doctor's permission, that we travel forward in time to investigate this curious event further, as I am sure you are aware that the existence of both myself and the other Sherlock Holmes here is theoretically impossible. In addition, I am curious to discover exactly what this Sherlock's Dr. Watson is like, as it is quite evident to me that a future counterpart of yourself also exists. Fascinating, isn't it?"

Watson's eyes bulged.

"Now, if you would be so kind," Holmes calmly nodded over to the Doctor. "We need to leave a marker. Something that cannot be removed or masked over a period of..."

"… Just over a century," Sherlock interjected. "It can't be a physical indicator - "

The Doctor leapt to his feet. " - because we need to be certain that it hasn't been replaced or replicated." He flipped his sonic screwdriver and pressed the end of it briefly to his chest before holding it up above his head. The tip of the screwdriver began to flash and whirr in a rhythm not entirely dissimilar to a heartbeat. "You two really are very clever," he said.

Watson dragged his fingers through his hair, and settled his face in his hands. "I am not entirely sure I follow."

"Don't worry, old fellow," Holmes said, unable to hide his amusement at his companion's confusion. "I trust you shall catch up in time. But I am afraid we have one more thing to do before we continue with the investigation." He casually made his way across the room to where Sherlock was now standing, and nodded at him. Sherlock nodded back.

Watson gaped in bewilderment as Holmes' fist suddenly collided with Sherlock's chin, and Sherlock's knee imbedded itself firmly into Holmes' stomach. The two men crumpled onto the floor.

Searching for any sign of clarification from the Doctor was a fruitless effort, as the man in tweed seemed more entertained by the event than shocked. Watson stammered and tried to find some way to voice his confusion, but the whole situation had baffled him beyond words - the unexpected fight between the Holmeses (Holmesae?) was the final straw.

From out of the chaotic mess, Holmes' hand raised weakly from the floor. "Wonderful! Most enlightening," he wheezed. "Watson, the game is afoot!"


	5. Chapter 5: Madness

_St. Bartholomew's Hospital, London.  
__Summer 2011._

John Watson's eyes were fixed on the man standing atop the old building. His hands were shaking, but still clutched the phone tightly to his ear.

Sherlock wasn't speaking. He heard the sound of something hard colliding with something else.

He had dropped the phone. He wasn't listening.

He was going to jump. Oh God.

Sherlock was going to jump.

In desperation, John called out from the street below.

"Sherlock!"

What use it would be, he didn't know. But it was something. It was the last thing he could possibly think of doing.

The man on the roof spread out his arms. What should he do? What could he do? Sherlock leaned forward. His body reached far beyond the point of recovering its balance.

"Sherlock..."

He fell.

The world seemed to freeze. John's blood turned to ice as he watched the man tumbling down from the roof.

His feet wouldn't let him stay. His mind couldn't focus.

He was a doctor. There was still something he could do.

Sherlock wouldn't die. He couldn't. The man was too stubborn to let something like this kill him.

John surged forward, building his pace as he clung ever tighter to that one hope.

He turned the corner and passed the building that had stood between himself and the fall.

...

His eyes widened.

He couldn't believe it. He really couldn't believe it.

The scene before him was beyond impossible.

He covered his face with his hands and took a huge breath.

"I know you've done some crazy things, Sherlock," he muttered under his breath, "but this is mad, even for you."

* * *

"Brilliant plan of yours, Sherlock. I mean, Sherlocks," the Doctor said as he ushered his three new companions out of the TARDIS. "Absolutely top notch. Simple, yet elaborate. Totally my kind of thing. You see, Doctor Watson, it's all quite elementary." He paused to see if he could get any kind of reaction from the two Sherlocks, but they appeared oblivious to his reference. "Oh well... Basically, we need a way to work out what all this... this Sherlock Holmesiness is all about, don't we? I mean, why are there two of them? At different times, but apparently on the same timeline? Do you see?"

The four men emerged onto a street not entirely dissimilar to the one they had left behind in old London, but for the fact that here it was mid-afternoon and somewhere in the early twenty-first century. Watson's reaction to everything happening around him was fascinating to watch.

"But that isn't all," the Doctor continued. "Oh no. See, we need to be sure that this is the same time line, right? Don't we, Sherlocks?"

"Quite," said Holmes, nursing his jawline.

Sherlock clutched his stomach. "Do shut up," he grumbled.

"Are you following all this, Watson? Because I don't want to have to go over something so... _elementary_ again," said the Doctor.

He paused.

"Nothing? Not even a giggle?" He frowned. "Oh, never mind. I thought it was funny. Now, where was I? Ah, yes. There are two factors, Watson. Two measureable factors we need to consider on this case. Time, and space."

Watson nodded, though his expression was entirely blank. "I... see," he said.

"Our minor conflict back at Baker Street was a method in which to determine the nature of our connection, albeit only to a small degree," said Holmes, his voice still a little hoarse from being kicked in the stomach. "By violently striking one another in different areas, we are able to determine, to a practical degree, our... unique relationship."

"And to what degree are you two connected, Holmes?" Watson looked at each of the three other men expectantly.

The Sherlocks muttered between one another in an attempt to find the suitable terminology.

"Psychosympathetic extrasensory perception," the Doctor gesticulated. "Or something else fancy and clever-sounding like that. Think of sympathy pains or telepathic links between twins. Only nothing like that at all, on account of these two being the same person."

Watson removed his hat and scratched his head. "I fear I might make myself sound quite the fool for asking, but... what exactly does that prove?"

"It proves two things," said Sherlock through gritted teeth. "For one, it proves that our connection extends beyond our names, places of residence, DNA structures and poor choice in intellectual companions. For all intents and purposes," Sherlock grimaced, "we can consider he and I to be exactly the same person."

"Which should, theoretically, be impossible," added Holmes.

The pair seemed thoroughly ruffled at the thought.

"And the second thing? You said that this proved two things," said Watson.

"It proves that both of me can hit very hard," Sherlock grumbled.

The Doctor chuckled. "Come on, chaps. That's only half the puzzle! We've still got lots of impossible stuff we need to deal with before we get this thing sorted out."

"I trust that our current course of action, then, has something to do with the other half. Perhaps something pertaining to that beacon you mentioned back at Baker Street," said Watson, pleased with himself for catching up to speed. He pondered for a moment before his eyes suddenly lit up. "My word! I think I'm following now. We're after the beacon you mentioned! This is London, but in the future. Am I correct?"

The Doctor and the Sherlocks exchanged glances ranging from amusement to utter disappointment. "I don't know why he even bothers listening," Sherlock muttered. "It's not like he's really trying to understand."

"Now, now," Holmes smiled. "Let us be patient with him."

"Well, you're almost right, Watson. But not at all at the same time," said the Doctor, pressing his hands together. "I think you might have missed the point."

Holmes' hand touched down on Watson's shoulder. "You see, old boy, we are here to determine if this is, indeed, the London that you and I know. The Doctor has already briefly explained this, but there are two factors at play here that must be weighed up in order to understand the gravity of the situation we are in, and to know exactly how to approach it. Those two factors are time and space. Given that both I and the other Sherlock here profess to be from different periods in time, it would be quite easy to assume that this world is the future incarnation of our own. However... Are you familiar with the multiverse theory?" He produced a small book, seemingly from nowhere, and pressed it into Watson's hands. "I cannot profess to be an expert on the matter, but I have idly perused this publication, and so have familiarised myself with the basics. Essentially, the theory can be summarised thusly - "

"For every event that takes place in our universe, there are an infinite number of ways in which that event could have potentially turned out," Sherlock interrupted. "The theory suggests that each of these potential outcomes occur at the exactly the same time, branching out into its own separate reality, creating an infinite number of universes running parallel to our own."

Watson's lips pursed. "Indeed," he said slowly, with knitted brows.

"Technically, it shouldn't be possible for the TARDIS to cross the barrier between alternate universes any more, but that's one explanation that could explain two Sherlocks," said the Doctor. "Now, keep all that parallel universe stuff in your mind. If the beacon is still present in Baker Street in this twenty-first century, that proves that both Sherlocks live in the same reality, which leaves us with the question - how are there two identical Sherlocks in one universe?"

"However," Holmes concluded," the alternative also leaves a pressing question unanswered. If the beacon is not present, then we can assume that this is indeed a parallel universe, which the Doctor here has already stated to be impossible to reach with the limitations the TARDIS possesses."

"Either way, it's a case that needs solving," said Sherlock. "Does that help?"

Still clearly confused, Watson nodded. "… I shall not delay our progression with any further questions. Let us hurry to Baker Street, then," he mumbled, tucking Holmes' book into his jacket.

"Capital suggestion, Watson."

The four of them continued snaking a path through the streets of London in relative silence, but for the occasional "fascinating" and "most singular" uttered by Holmes as he occasionally admired the twenty-first century trivialities that they passed, such as passing cars or people checking their mobile phones.

However, as they grew closer to Baker Street, the quiet became considerably more heavy. It was apparent that Sherlock was getting rattled at something, as his pace seemed to quicken, his hands twitching and nervously seeking each other out as he moved forwards.

As their destination finally came into view, the three other men could see Sherlock freeze in place. He turned on his heels and sniffed the air, his eyes darting everywhere as he surveyed the street in minute detail. He mumbled something under his breath, took a few steps forward, craned his neck upwards to scan the windows of the buildings around them.

He turned about furiously to face the Doctor.

"You brought us back to the same date," he growled. "Why did you bring us back to the same date?"

"Very observant," said the Doctor, grinning. "How'd you work that out?"

Sherlock leapt forward and grabbed the Doctor's shoulders. "_Why_?"

The Doctor shrugged. "The coordinates were still recorded in the data core of the TARDIS. It made sense to use it as a reference point."

"You idiot. You _absolute idiot!_"

"Have I missed something?" said the Doctor. "I thought it would be the easiest way to compare - "

"Everyone is in danger. Everyone is going to die. If anyone sees me here, alive..." Sherlock stopped and drew a long, shuddering breath. His eyes widened in horror. "John," he murmured. His hands fell from the Doctor's shoulders and, in a single movement, he swept himself right around to face the direction they had come from. He pointed in the direction of 221B and shot a horrible, venomous look at the three other men. "Mrs Hudson," he hissed. "_Protect her_."

With that, he disappeared back down the street, his coat billowing behind him.

The Doctor stared at the space where Sherlock had been standing only moments before.

"What does he mean?" Watson puzzled. "Why should everyone be in danger?"

Holmes produced his pipe from his jacket pocket, lit it, and put it to his lips. He frowned. "I believe we may have stumbled into a case that the other Sherlock has not yet closed," he said. "A most personal case."

"But why should Mrs Hudson be in peril? And... John..." Watson shivered. "Is he referring to another John Watson? Is... is this London's John Watson in danger as well?"

Holmes nodded. "It would be safe to assume so."

It took a few seconds for everything to click.

Watson staggered backwards. "Holmes... When you and... and the other Sherlock Holmes struck one another, you both felt the pain of both blows. You felt the pain that the other Sherlock suffered."

"Yes," said Holmes, darkly. "I did."

"In that case... if we are to assume that I possess the same connections with this John Watson as you do with this Sherlock..." He faltered.

"I think it would be best to ask that man," said Holmes. He pointed his pipe at the Doctor, who was still staring, dumbfounded, into empty space. "He has considerably more experience with situations such as these."

Watson stepped up to the Doctor, wringing his hands. "Well, Doctor?"

The Doctor's mouth opened a fraction. Slowly, his eyes came to focus on Watson.

He flipped the sonic screwdriver into Watson's hands.

"Mrs Hudson needs to be protected at all cost. Go in there. Don't let anyone touch her. And keep the screwdriver with you. You just point it and think. Press that there," he pointed at the device, "and listen for a thumping noise." The Doctor patted the man firmly on the shoulder and turned him in place to face 221B.

"But... Doctor..."

"You," the Doctor swiveled and jabbed a finger at Holmes. "Come with me." He bounded forwards and hooked Holmes under the arm, and pulled both himself and the detective in the direction Sherlock had taken.

"Doctor," Watson pleaded. "What will happen to me?"

The Doctor slowed and let go of Holmes' arm. He shook his head at Watson. "Nothing will happen to you," he said. "Nothing. You'll be fine. You go in there and protect Mrs Hudson. You will be fine," he repeated. He smiled, but his eyes didn't appear to correspond with his expression. "I promise."

The Doctor and Holmes fled back down the street Sherlock had also taken, leaving Watson alone.

Watson looked at the sonic screwdriver in his hand.

He closed his eyes.

"This is madness," he said.

He held up the screwdriver and pressed the little switch. The tip glowed green, just as it had in the Doctor's hand.

His heart jittering in his chest, he made his way towards the flat. He stepped up to the door and exhaled shakily through his nostrils.

"Absolute madness," he said.

He knocked the door and waited.


End file.
